Much has been learned in recent years about the mechanisms by which breastfeeding improves child health and survival. However, there has been little progress in using these insights to improve pediatric care. Factors that are important for protecting the breast fed infant might be expected to decrease the adverse effects of weaning on diarrhea, growth, and development. The proposed study is meant to begin addressing this important gap by a clinical trial of lactoferrin supplementation in previously weaned children. Lactoferrin, an iron-binding protein with multiple physiological functions (anti-microbial, anti-inflammatory, and immunomodulatory), is one of the most important proteins present in mammalian milk. Our hypothesis is that lactoferrin (given as a daily supplement in amounts similar to those consumed if the child were still breast fed) will improve health by mimicking its protective roles in milk. There is a vast literature showing in vitro and animal model benefits of lactoferrin. For the last 27 years we have been working on understanding the protective factors in milk. Our recent studies have focused on lactoferrin. We have found that lactoferrin not only inhibits growth;it impairs virulence by causing loss of attachment/invasion structures in multiple bacterial enteropathogens. The proposed community-based study will be conducted in a previously weaned population at risk for repeated intestinal infections. Infants who are 12-24 months of age living in the District of Independencia, Lima, Peru will be eligible for enrollment. We will conduct a randomized double blind placebo controlled trial comparing twice daily supplementation with bovine lactoferrin versus a placebo (maltodextrin). Therapy will be continued for 12 months with close monitoring of all study participants for diarrhea and growth. Specific aim 1: Determine the effect of bovine lactoferrin supplementation on prevention of diarrhea, measured by the number of episodes of diarrhea during a 12 month trial in previously weaned Peruvian children enrolled at 12 to 24 months of age. Specific aim 2: Determine the effect of bovine lactoferrin supplementation on growth. The significance of these studies is that they will prove feasibility of improving child health after the end of breastfeeding by continuing ingestion of a major protective milk protein. Diarrhea and malnutrition after weaning is a global problem that may be amenable to this approach.